1. Field of Art
The present disclosure relates to a finder optical system and an image pickup apparatus including the same. The present disclosure specifically relates to a finder optical system and a light metering optical system which are suitable for an image pickup apparatus such as a single-lens reflex camera. The finder optical system includes an eyepiece optical system and a light metering optical system. The eyepiece optical system allows an observer to observe an object image formed on a focusing screen. The light metering optical system is configured to re-image the object image formed on the focusing screen on an image sensor to provide an electronic image.
2. Description of the Related Art
In a finder optical system in Japanese Patent Application Laid-Open No. 2007-93888, an electronic image is obtained by re-imaging an object image formed on a focusing screen on an image sensor in a light metering optical system via an erecting optical system. The finder optical system has a function of recognizing a face of an object and adjusting focus and exposure, a function of moving a focusing point along with movement of the object, and a function of displaying the object image in real time on a liquid crystal screen provided on a back surface of a camera body. The finder optical system in Japanese Patent Application Laid-Open No. 2007-93888 also includes on a light exit side of a pentagonal prism a light path dividing unit. The light path dividing unit is a half mirror for dividing a light path into a path for guiding light to the image sensor via the light metering optical system and a path for guiding light to an eyepiece optical system.
Also is known a camera light metering apparatus in which light receiving lenses constituting an eyepiece optical system and a light metering optical system are arranged side by side on a side of a light exit surface of a pentagonal roof prism. In Japanese Patent Application Laid-Open No. 63-74042, a light metering lens including an inner reflection surface is used as the light metering optical system to guide a light flux exiting from the pentagonal roof prism to a light receiving element.
To pick up a bright and high-quality electronic image at the time of picking up an image by forming an object image on the image sensor with use of the light metering optical system, a bright light metering optical system and a high-pixel-number and large-sized image sensor are required.
On the other hand, to observe the object image formed on a focusing screen in a bright state, a large-diameter lens needs to be used for the eyepiece optical system.
To pick up a high-quality image in real time and observe a bright object image via the eyepiece optical system, the light metering optical system including the large-sized image sensor and the large-diameter eyepiece optical system must be arranged side by side on the light exit side of an erecting optical system. However, the image sensor and the eyepiece optical system mechanically interfere with each other, which makes it difficult to dispose both of them.
As shown in the light metering apparatus in Japanese Patent Application Laid-Open No. 63-74042, by inclining an optical axis of the light metering optical system toward an optical axis of the eyepiece optical system, mutual interference can be avoided easily. However, when the object image formed on the focusing screen is re-imaged on the image sensor in a state in which the optical axis of the light metering optical system is inclined toward a normal line of the focusing screen, asymmetric curvature of field and astigmatism occur depending on an image height, which makes it difficult to pick up a high-quality image.